# packcircles

R package for circle packing. Algorithms to find arrangements of non-overlapping circles

This package provides functions to find non-overlapping arrangements of circles.

The function `circleRepelLayout` attempts to arrange a set of circles of specified radii within a rectangle such that there is no-overlap between circles. The algorithm is adapted from an example written in Processing by Sean McCullough (which no longer seems to be available online). It involves iterative pair-repulsion, in which overlapping circles move away from each other. The distance moved by each circle is proportional to the radius of the other to approximate inertia (very loosely), so that when a small circle is overlapped by a large circle, the small circle moves furthest. This process is repeated iteratively until no more movement takes place (acceptable layout) or a maximum number of iterations is reached (layout failure). To avoid edge effects, the bounding rectangle is treated as a toroid. Each circle’s centre is constrained to lie within the rectangle but its edges are allowed to extend outside.

The function `circleProgressiveLayout` arranges a set of circles, which are denoted by their sizes, by consecutively placing each circle externally tangent to two previously placed circles while avoiding overlaps. It was adapted from a version written in C by Peter Menzel. The underlying algorithm is described in the paper: Visualization of large hierarchical data by circle packing by Weixin Wang et al. (2006).

The function `circleRemoveOverlaps` takes an initial set of overlapping circles and attempts to find a non-overlapping subset or, optionally, a subset with some specified degree of overlap. Circle positions remain fixed. It provides several fast heuristic algorithms to choose from, as well as two based on linear programming. For the latter, package lpSolve must be installed.

The function `circleGraphLayout` is an initial Rcpp port of an algorithm described by Collins and Stephenson (2003) to find an arrangement of circles which corresponds to a graph of desired circle tangencies. The implementation is based on a Python version by David Eppstein (see CirclePack.py in the PADS library.

To install:

• the latest released version: `install.packages("packcircles")`
• the latest development version: `install_github("mbedward/packcircles")`

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